Velutina prolongata, a marine snail. We've only encountered this species a few times in the low intertidal zone on Bodega Head. The Light & Smith Manual says they're mainly subtidal. These are two different individuals — the first two photos from July 2012 and the last two from June 2011. They were both ~1 cm long.
Note the orange tips of the tentacles and the narrow orange border on the foot. There's a very pretty checkerboard pattern (alternating gray and white mottling) along the edge of the mantle (next photo).
In the photo above, the lighting is such that you can see through the thin shell. The slightly curved leaf-like structure is a gill.
The next two photos show the abalone-like shape of the shell (but lacking respiratory pores). Most of the shell is a very large, expanded body whorl, while the uppermost whorls are tiny and positioned at one end of the shell (see last photo).
I haven't been able to find very much information about this attractive snail. Other species of Velutina have been reported feeding on tunicates or hydroids. [A smaller, less colorful species of Velutina is more common on Bodega Head — more about that species in a future post!]